1. Field of the Invention
This invention relates to novel ethylene/xcex1-olefin copolymers. More particularly, it relates to ethylene/xcex1-olefin copolymers which are excellent in transparency and gloss, show high blocking resistance and exhibit well-balanced modulus and strength when processed into films by blown film extrusion.
2. Description of the Related Art
It has been a practice to produce copolymers of ethylene with xcex1-olefins by the polymerization mainly using Zeigler-Natta catalysts. Blown Films of these copolymers are excellent in mechanical characteristics (tensile strength, impact strength, etc.) and, therefore, used in a large amount for various purposes, for example, bags.
However, blown films of these ethylene/xcex1-olefin copolymers alone suffer from a problem of showing poor transparency.
Therefore, it has been a practice in the field with a need for high transparency to blend these ethylene/xcex1-olefin copolymers with low-density polyethylene produced by the high-pressure-process (hereinafter referred to simply as HPLD) which has an excellent effect of improving transparency to thereby ensure high transparency. However, this method brings about an increase in the production cost of the resin compositions. From the viewpoint of physical properties, moreover, there arise several problems, for example, a decrease in strength and worsening of blocking resistance in association with an increase in transparency.
Ethylene/xcex1-olefin copolymers produced by the polymerization using metallocene catalysts, which have been employed in recent years, are superior in transparency in the low density region (density; 0.918 or less) to the ethylene/xcex1-olefin copolymers obtained by using Ziegler-Natta catalysts. However, the transparency of the former ethylene/xcex1-olefin copolymers is worsened with an increase in density. Thus, the ethylene/xcex1-olefin copolymers having a density of 0.918 or more, which are commonly employed as packing films, cannot show any sufficient transparency. In the field with a need for high transparency, therefore, it is also needed to blend these copolymers with HPLD.
In addition, no sufficient transparency cannot be established even by elevating the molecular weight by performing the multi-stage polymerization as proposed by JP-A-3-23717 or by using two or more metallocene compounds as proposed by JP-A-5-155932 and JP-A-60-35006 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d).
Further, JP-A-10-168130 points out that the transparency can be improved by regulating the storage modulus and loss modulus each in a definite range. Even in this case, it is scarcely possible to establish such performance satisfying the requirement in the field with a need for high transparency.
Therefore, it has been urgently required to develop an ethylene/xcex1-olefin copolymer whereby these problems can be solved. However, it is impossible by the related art not only to obtain a ethylene/xcex1-olefin copolymer which can be processed into films with sufficient transparency but also to clarify the polymer structure for achieving this object.
This invention aims at providing ethylene/xcex1-olefin copolymers which show sufficient transparency and excellent mechanical properties (modulus, strength, etc.), processing properties, blocking resistance, heat sealing properties and heat sealing strength when processed into films by blown film extrusion.
The inventors have conducted extensive studies to solve the above problems. As a result, they have made it possible to uniformly form components of ethylene/xcex1-olefin copolymers for improving the transparency, compared with the related art.
Further, the inventors have clarified components worsening the transparency.
Furthermore, they have successfully found out that ethylene/xcex1-olefin copolymers with excellent transparency can be obtained by elevating the balance between the improving components and the worsening components to such an extent which cannot be achieved by the related art and regulating the contents of these components each within a definite range, thereby completing the invention.
Accordingly, the ethylene/xcex1-olefin copolymer of the invention is a copolymer of ethylene with an xcex1-olefin having 3 to 20 carbon atoms characterized by satisfying the following physical properties (a) to (d):
(a) having a density of 0.900 to 0.965 g/cm3;
(b) having a melt index (MI; 190xc2x0 C., under a 2.16 kg load) of 0.01 to 100 g/10 min;
(c) in a chromatogram with the use of Rayleigh ratio obtained by extrapolating GPC-MALLS (Gel Permeation Chromatography-Multi Angle Laser Light Scattering detector) data at a scattering angle of 0xc2x0, showing an average of Mc: {overscore (Mc)} obtained by the xe2x80x9cfive-point measurement methodxe2x80x9d of 0.5% or more and a standard deviation  less than "sgr" greater than  from the average of 35% or less, wherein Mc stands for the chromatographic area ratio of the components having molecular weight of 1,000,000 or more calculated on the basis of the above measurement; and
(d) having a W30 (weight fraction of the portion eluted from TREF column below) in CFC measurement of 1 (% by weight) or less.
The ethylene/xcex1-olefin copolymer according to the invention is characterized by satisfying the following requirement (e), in addition to the above-described requirements (a) to (d):
(e) having a flow ratio FR (=I10kg/I2.16kg) of 7.0 or less, wherein I10kg stands for the melt index measured at 190xc2x0 C. under a 10 kg load and I2.16kg stands for the melt index measured at 190xc2x0 C. under a 2.16 kg load.
The ethylene/xcex1-olefin copolymer according to the invention is characterized by satisfying the following requirements (f) or the requirements (e) and (f), in addition to the above-described requirements (a) to (d):
(f) having a ratio Mw/Mn of 1.5 to 3.5, wherein Mw stands for the weight-average molecular weight obtained by GPC measurement and Mn stands for the number-average molecular weight.
The ethylene/xcex1-olefin copolymer according to the invention is an ethylene/xcex1-olefin copolymer satisfying the above-described requirements (a) to (d), (a) to (e), (a) to (d) and (f), or (a) to (f), characterized by having a density of 0.918 (g/cm3) or less.
Further, the ethylene/xcex1-olefin copolymer according to the invention is an ethylene/xcex1-olefin copolymer satisfying the above-described requirements (a) to (d), (a) to (e), (a) to (d) and (f), or (a) to (f), characterized by having a density of 0.918 (g/cm3) or more and satisfying the following requirements (g):
(g) having Mc and W74 (weight fraction (% by weight) of the portion eluted from TREF column below 74xc2x0 C.) in CFC measurement satisfying the following relationship (i):
W74 less than 5.5Log {Mc}+15xe2x80x83xe2x80x83(i).
Furthermore, the ethylene/xcex1-olefin copolymer according to the invention is an ethylene/xcex1-olefin copolymer satisfying the following physical properties (axe2x80x2) to (dxe2x80x2):
(axe2x80x2) having a density of 0.900 to 0.955 g/cm3;
(bxe2x80x2) having a melt index (MI; 190xc2x0 C., under a 2.16 kg load) of 0.01 to 100 g/10 min;
(cxe2x80x2) in a chromatogram with the use of Rayleigh ratio obtained by extrapolating GPC-MALLS data at a scattering angle of 0xc2x0, showing a chromatographic area ratio of the components having molecular weight of 1,000,000 or more, calculated on the basis of the above measurement, of 1% or more; and
(dxe2x80x2) having Mc and W74 (weight fraction (% by weight) of the portion eluted from TREF column below 74xc2x0 C. ) in CFC measurement satisfying, the following relationship (ii):
W74 less than 5.5Log {Mc}+10xe2x80x83xe2x80x83(ii).
The film according to the invention is processed by extruding the ethylene/xcex1-olefin copolymer as described above.